The present invention disclosed herein relates to an alternative current (AC) direct drive light emitting diode (LED) power supply capable of handling an overvoltage, and more particularly, to an AC direct driver LED power supply, when an overvoltage exceeding a reference voltage is instantaneously or continuously supplied, effectively controlling a current for each phase according to a voltage to minimize heat emission and to prevent a damage of an LED light source caused by the overvoltage by reducing a power load on the power supply, thereby providing safety of a power supply unit and simultaneously providing high efficiency and a high power factor.
Recently, light emitting diodes (LEDs) largely increase in brightness, have a longer life and a smaller energy consumption amount than other general lightings such as incandescent lamps and fluorescent lamps, and are echo-friendly, which are considered as alternative lighting sources of general lighting devices.
Generally, LED drive devices using an alternative current are designed to be formed of a serial array of a plurality of LEDs with appropriate intervals and to allow a voltage thereof is set up and controlled using a switch controlled by a current.
General LED drive devise using constant current circuits have a structure, in which a plurality of constant current circuits having different current values are formed for each stage to provide current properties as a stepped shape. Korean Patent Registration No. 10-1064906 (registered on Sep. 7, 2011) discloses “LED lighting device”, which shows a similar example.
FIG. 1 is a circuit diagram of a general LED drive constant current circuit having a multistage structure. As shown in FIG. 1, a power supply input 11 receiving an applied AC voltage converts the AC voltage into a direct current (DC) voltage using a rectifier part 12 and inputs the DC voltage into LED arrays 31, 32, and 33 including a plurality of LEDs. That is, as shown in FIGS. 2A, 2B, and 2C, a waveform A of a voltage passing through the rectifier part 12 is shown as a waveform B of an input current passing through constant current control parts 21, 22, and 23.
In this case, a corresponding undulating voltage is allowed to flow less than a rated current defined by constant current control parts 21, 22, and 23 to protect an LED. However, when a voltage higher than a reference voltage is inputted, a voltage exceeding a voltage set up by the LED is to be managed by a drive unit. Due thereto, the drive unit consumes power corresponding to a value obtained by multiplying an exceeding amount of the voltage by a current defined by the drive unit, thereby causing overheating.
FIGS. 2A, 2B, and 2B are waveform diagrams of the general LED drive constant current circuit having a multistage structure. As shown in FIGS. 2A, 2B, and 2C, a waveform through a power supply using the constant current circuit using a plurality of stages shown in FIG. 1 is controlled as shown in FIG. 2A and a current according to a voltage A is controlled to be a current B having a multistage structure. The general waveform structure, differing according to an environment, additionally includes a circuit corresponding to an overvoltage occurring in an AC power source.
That is, FIG. 2B shows a form of a current C while a protection circuit is not operating, and a current D while the protection circuit is operating. That is, when the protection circuit operates in a form of the current C having a multistage structure, the current C of the constant current drive unit shows the form of the current D entirely reduced.
Also, FIG. 2C shows, in a waveform of a voltage E generated with the overvoltage, a flow of a current F instantaneously disconnecting a current in a section, in which the overvoltage occurs. According thereto, generally, a protection circuit is design to correspond to an overvoltage in a manner of (b) or (c) in FIG. 2.
However, as shown in FIG. 2B, a method of entirely decreasing a current has a limitation, in which heat emission occurring due to a continuous overvoltage may cause a problem in a system. Also, as shown in FIG. 2C, a method of disconnecting a current has a limitation, in which a flicker phenomenon partially occurs to make intensity of illumination of an LED module unstable.
FIGS. 3A and 3B are circuit diagrams of a general constant current circuit of one stage of a constant current drive circuit having a multistage structure, and FIG. 4 is a waveform diagram of the general constant current circuit of one stage of the constant current drive circuit having the multistage structure. The structure of the constant current circuit of FIG. 1 may not only be applied to a multistage structure but may be applied to a case of FIGS. 3 and 4 formed of one constant current circuit as a protection circuit. Also, the structure may be applied as constant current circuits of all stages or some stages.